INVESTIGATION WITH A ROCK-SALT PRISM. 87 



compound the CH3 and the NOo groups occur in the ortho, mcta, and 

 para positions. The latter is a crystalline solid, hence very opaque, 

 due to scattering of the light. 



In this compound no shifting occurs, except at 13.6/^ and 13.8/i,, which 

 appears to be accidental. If this shifting is due to a resonance of simi- 

 lar groups of particles, as already mentioned under the xylenes, then 

 one would not expect a shifting of the bands in these two compounds. 



To test this theory of resonance, dinitrobenzene, CeH4(N02)2, or 

 some other benzene derivative having two similar groups of atoms, will 

 have to be examined. Unfortunately these compounds are solids, hence 

 difficult to examine in thin films. 



These compounds are so complex that little can be accomplished in 

 studying them. Thus, in the region at 6 /a to 7 /* the bands of the ben- 

 zene, the CH3, and the NO2 ions are superposed, and the result is great 

 opacity. In the para compound the groups seem to have greater free- 

 dom, and the 6.86 ix of CH3 compounds and the 9.08 /u, of NO2 com- 

 pounds are more apparent; also the 3.25 /x, 8.7 /i, and 11.9/1 bands of 

 benzene are more conspicuous. The 3.43 /m, 6.86 /x, and 13.8/1 bands 

 are to be noticed, since they appear by the addition of a single CH3 

 group, just as in toluene. The 6.25 /a band occurs only as a slight asym- 

 metry. The 9.08 /A band is the only one in common with the five NOj 

 compounds studied. 



PHENOLS. 



Phenol. CeH^OH. (Fig. 99.) 



The phenols are oxygen derivatives of benzene, which in their chem- 

 ical character stand between the alcohols and the acids. 



Phenol, or phenyl alcohol, melts at 44°, and hence could be kept liquid 

 before the spectrometer slit. Unfortunately, time did not permit an 

 examination beyond 8 /*, using the small spectrometer. With the large 

 spectrometer the regions at 3 /* and 6/1 to 7/1 were examined. The 

 3.25 fx. band of benzene is almost obliterated by the much stronger band 

 at 2.97 /x. The bands at 6.23 /i and 6.75 /a of benzene are not disturbed. 

 The 6.23 /x band is much more prominent than in benzene. This 

 strengthening of the 6.23 /x band and the weakening of the 3.25 /x con- 

 firm the belief, frequently mentioned in this paper, that when an H atom 

 is replaced by a different atom, or group of atoms, the result does not 

 seem to show so much the introduction of new lines as it does a condi- 

 tion of the molecule whereby the original bands are strengthened or 

 weakened. 



Whether the 2.95 /x band is due to the OH-group will be discussed 

 elsewhere. The absence of the 6/x band would indicate that the one 

 at 2.Q^ /x is characteristic of the alcohols and the phenols. 



